The use of gaseous catalysts, and especially tertiary amines, as curing agents in the cold box process of curing phenol formaldehyde and poly-isocyanate resins is known in the art.
Published US application 2010/0126690, to van Hemelryck, teaches that some of the preferred tertiary amines are trimethyl amine (“TMA”, CAS RN 75-50-3), dimethyl ethyl amine (“DMEA”, CAS 75-64-9), dimethylisopropylamine (“DMIPA”, CAS 996-35-0), dimethyl propylamine (“DMPA”, CAS RN 926-63-6) and triethyl amine (“TEA”, CAS RN 121-44-8). The '690 published application teaches that, while these tertiary amines have been taught in the past as being used individually, it is possible to use the tertiary amines in blends. The blends are typically binary, but can comprise more than two tertiary amines.
The '690 published application also teaches that the preferred boiling point of the amine is below 100° C., at least when the amine is used individually, to permit evaporation and to achieve satisfactory concentration of amine in the gas mixture injected. This guideline also helps to avoid condensation of the amine in the mold.
In addition to the upper limit, there is also a lower limit of preferred boiling point. For example, TMA is a gas at ambient temperatures (bp of about 3° C.), making it more difficult to handle than the higher boiling amines. The lower molecular weight amines in general, with DMEA (bp of 44-46° C.) as a specific example, tend to have a strong ammonia odor, making them unpleasant to work with. At the other end of the boiling point spectrum, TEA (bp of 89° C.) tends to condense out of the gas mixture, especially in the winter, indicating the practical upper limit for boiling point is well below 100° C.
A parameter related to boiling point is molecular weight, which must be low enough to permit ready diffusion of the gaseous amine through the foundry mix. The '690 published application teaches that TEA (Mw 101) is at the high end of the acceptable range for the cold box process. The '690 published application teaches that a good set of acceptable curing catalysts include the set of tertiary amines with 5 carbon atoms consisting of DMIPA (bp of 64-67° C.), DMPA and N,N-diethylmethylamine (“DEMA”, CAS RN 616-39-7).
In spite of the increasing understanding of these tertiary amines and their function as curing catalysts, it is still unknown how to best use the amines, especially in combinations that are not strictly mixtures.